pred·ni·sone (pr?d?n?-s?n?,-z?n?)n. A synthetic corticosteroid, C21H26O5, derived from cortisone and used as an antiallergy, immunosuppressive, and anti-inflammatory drug.[pre(gnane), a steroid (from pregnant) + d(i-) + -(e)n(e) + (cort)isone.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.prednisone (?pr?dn??s??n) n (Pharmacology) a steroid drug derived from cortisone and having the same uses[C20: perhaps from pre(gnant) + -d(ie)n(e) + (cort)isone]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014pred?ni?sone (?pr?d n??so?n, -?zo?n) n. an analog of cortisone, C21H26O5, used in tablet form chiefly for treating allergies, autoimmune diseases, and certain cancers. [1950?55; pre(gna)d(ie)n(e), a component of its chemical name + (cort) isone] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.